SANSUI 800 Rebuild - Tuning Meter Help

[JB8]

Sansuist!

After some much-appreciated assistance from some of you, I recently completed a successful refurb of my first Sansui, a 2000. The results were astonishing and I will not be selling the unit, like, ever. The sound is phenomenal in my opinion. So, I figured I try my luck with another popular low-powered unit, the 800, and it's going great. Recap is completed for most boards except for the AM and FM blocks and the FM MPX, which I may not touch, reception is great and I'm always cautious when it comes to those boards. Unit is sounding great, has next to no DC at the speaker terminals, I have yet to dial in the idle, but for now it's purring nicely.

The only thing that's not working properly at this point is the tuning meter, so I'd love to get some basic trouble shooting ideas and next steps. Here's what I know:

• It's not stuck - if I attach the DMM (in ohms) across the positive terminal, neg lead to chassis ground, the meter pegs
• If, with power off, I check ohms across the meter terminal I get 1.2K ohms
• Adjusting VR201 doesn't have any effect on the meter but I am seeing changes in ohms across the VR when making adjustments
• VD202 tests fine
• I have continuity from the pos terminal of the meter to the function switch
• I'm getting nice stereo sound/separation and the beacon is lighting up as it should

Any coaching would be awesome, no hurry, thanks in advance!

 

[davefr]

It looks like TR206 is the transistor that drives the meter in FM Auto. That would be the next thing I'd check.

 

[JB8]

Thanks for jumping in davefr, much appreciated!

Checking TR206 in circuit revealed what seemed to be an E-C short, bingo? Unfortunately no, tested fine when I pulled it but I still replaced it just in case (KSC1845F). No change and I'm not getting any voltage at the collector, should be 6.5v DC.

This is where my signal tracing sucks, I'm assuming I'll need to trace backwards to find out where the voltage is dropping out?

TR206 voltages were all (ECB) at 0 v DC. Also getting no voltage on either side of D203.

I also tested TR205 as a reference and found the following:

E -- 9.5v DC (should be 3.5v)
C -- 9.5v DC (should be 11.9v)
B -- 3.98v DC (should be 3.8v)

 

[davefr]

I think I misread the schematic. The meter is fed by VD202. (not TR206) I'd test VD202 and D203. I'd also make sure the external 2J wire is going to S1 and 2G is going to B+. Also check VR201.

I might also put a DC meter across the signal meter and toggle between a strong stereo station and dead zone and then work back to see where the signal is failing.

Hopefully other guys that know these circuits well will chime in.

 

[JB8]

VD202 and D203 are testing fine but show no current flow, seems I don't have any power downstream from TR205, perhaps T205 is bad? That entire lower right hand corner of the board isn't testing for any voltage on any of the components but I'm getting lots of current everywhere else.

I'll keep poking around and update soon. Thanks again!

 

[JB8]

Quick update, I've done some probing to check components and voltages, here's where I'm at:

• Still no voltage feeding D203, so since I have power at TR205 (results in post #3) I'm assuming there's an issue with T205 (?)
• R234 and R217 test fine and I replaced C233 for good measure (tested at 2.1uF out of chassis but wasn't the issue)
• I'm getting 10v DC at 2E(F), no voltage at 2J, I have continuity from 2G to the switch (S1) and on to the meter itself

Am I barking up the wrong tree assuming T205 should be feeding the flow to the meter?

EDIT: Well this was a miss... I'm also getting no signal when S3 is in the Mute position, regardless of the signal strength. No stereo light, no nothin when in the Mute position, FM only comes through when in MPX Noise Canceling. I imagine this is significant to the issue, or, it could be a result of the issue but it's certainly worth noting either way. And one last thing worth noting, I'm getting a tiny bit of signal passing with the volume knob at zero (across all functions and after having cleaned the pot a few times).

 

[JB8]

Update. Mute position is producing FM signal, but no stereo beacon when in this position and no tuning meter action in either Mute or MPX positions.

If someone can just point me in the right direction I'll do my best to track this down once I better understand what I'm looking for. All of the above info is accurate.

Thanks in advance for lending a hand, would really appreciate some help.

 

[JB8]

I'm going to keep pumping this thread just in case someone wants to jump in, ha!

New observation - when listening to FM in MPX position, strong clear sound in stereo with beacon lit, when I switch to Muting position the beacon dims completely then has a small, brief audible surge that's also reflected in the beacon, then the beacon goes nearly dark but remains on slightly, audio is significantly lower volume and a bit of consistent distortion is introduced. This is with the antenna switch on the back in the DIST position. When in LOC the beacon just goes dark, no surge. (And yes, the switch has been cleaned)

I'll be here, will likely just keep posting, who knows, maybe I'll miraculously figure it out on my own, we'll see.

 

[JB8]

FYI - I found another thread with a similar issue and hopped into the mix to ask for some advice. Turns out TR205 was bad so hopefully after replacing it all will be good, sweet!